全文获取类型
收费全文 | 16548篇 |
免费 | 316篇 |
国内免费 | 35篇 |
专业分类
电工技术 | 191篇 |
综合类 | 17篇 |
化学工业 | 1891篇 |
金属工艺 | 272篇 |
机械仪表 | 308篇 |
建筑科学 | 475篇 |
矿业工程 | 23篇 |
能源动力 | 242篇 |
轻工业 | 1606篇 |
水利工程 | 107篇 |
石油天然气 | 31篇 |
无线电 | 1376篇 |
一般工业技术 | 1842篇 |
冶金工业 | 6776篇 |
原子能技术 | 166篇 |
自动化技术 | 1576篇 |
出版年
2022年 | 105篇 |
2021年 | 189篇 |
2020年 | 114篇 |
2019年 | 165篇 |
2018年 | 202篇 |
2017年 | 196篇 |
2016年 | 239篇 |
2015年 | 140篇 |
2014年 | 267篇 |
2013年 | 594篇 |
2012年 | 450篇 |
2011年 | 565篇 |
2010年 | 451篇 |
2009年 | 441篇 |
2008年 | 502篇 |
2007年 | 495篇 |
2006年 | 404篇 |
2005年 | 405篇 |
2004年 | 321篇 |
2003年 | 321篇 |
2002年 | 287篇 |
2001年 | 295篇 |
2000年 | 283篇 |
1999年 | 420篇 |
1998年 | 2038篇 |
1997年 | 1196篇 |
1996年 | 903篇 |
1995年 | 576篇 |
1994年 | 466篇 |
1993年 | 526篇 |
1992年 | 191篇 |
1991年 | 196篇 |
1990年 | 212篇 |
1989年 | 235篇 |
1988年 | 182篇 |
1987年 | 177篇 |
1986年 | 164篇 |
1985年 | 218篇 |
1984年 | 110篇 |
1983年 | 100篇 |
1982年 | 94篇 |
1981年 | 112篇 |
1980年 | 126篇 |
1979年 | 93篇 |
1978年 | 54篇 |
1977年 | 200篇 |
1976年 | 396篇 |
1975年 | 61篇 |
1974年 | 42篇 |
1973年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
BW Woodward JW Mabry MT See JK Bertrand LL Benyshek 《Canadian Metallurgical Quarterly》1993,71(8):2040-2046
An animal model and computer software were developed to conduct across-herd genetic evaluations using data from producers participating in the Sow Productivity Index program of the American Yorkshire Club. The final data set consisted of 61,596 litter records from 1986 to early 1990. The animal model included fixed contemporary group effects and random additive direct, service sire, permanent environmental, and residual effects. Additive genetic relationships among animals were included. A separate relationship matrix for service sires and their sires was also included. A data set similar to the Yorkshire field data was simulated to use in testing the animal model. The simulated data set consisted of 40 herds, each with 120 reproducing dams and either four or five sires. Six generations of simulated data were produced, resulting in 20,605 litter records. These records were then evaluated using the animal model for number of pigs born alive. Finally, correlations between the true breeding values from the simulation and the predicted breeding values were computed. The correlation between the 918 true and predicted sire breeding values was considerably lower for the animal model without a service sire effect than when it was included (.53 vs .74, respectively). However, the difference was cut in half (.66 vs .77) when only sires with greater than five daughter records were included. The high accuracy of the animal model with a random service sire effect indicates that the proposed model adequately accounts for the variation found in records for number of pigs born alive. 相似文献
82.
83.
JL Van Laethem M Cremer MO Peny M Delhaye J Devière 《Canadian Metallurgical Quarterly》1998,43(6):747-751
Microcapsules are used for the formulation of drug controlled release and drug targeting dosage forms. Encapsulated hydrophobic drugs are often applied as their solutions in plant oils. The uptake of the oils in the complex coacervate microcapsules can be improved by the addition of surfactants. In this study, soybean, olive and peanut oils were chosen as the representatives of plant oils. The well characterized complex coacervation of gelatin and acacia has been used to produce the microcapsules. The amount of encapsulated oil has been determined gravimetrically. The encapsulation of the oils was high (75-80%). When the surfactants with HLB values from 1.8 to 6.7 were used, the amount of encapsulated oil was high (65-85%). A significant decrease of the oil content in the microcapsules was found when Tween 61 with HLB = 9.6 had been added into the mixture. No oil was found inside the microcapsules from the coacervate emulsion mixture containing Tween 81 (HLB = 10) and Tween 80 (HLB = 15), respectively. The results of the experiment confirm the dependence of hydrophobic substance encapsulation on the HLB published recently for Squalan. 相似文献
84.
J Oldenhof R Vickery M Anafi J Oak A Ray O Schoots T Pawson M von Zastrow HH Van Tol 《Canadian Metallurgical Quarterly》1998,37(45):15726-15736
The dopamine D4 receptor is a G protein-coupled receptor (GPCR) that belongs to the dopamine D2-like receptor family. Functionally, the D2-like receptors are characterized by their ability to inhibit adenylyl cyclase. The dopamine D4 receptor as well as many other catecholaminergic receptors contain several putative SH3 binding domains. Most of these sites in the D4 receptor are located in a polymorphic repeat sequence and flanking sequences in the third intracellular loop. Here we demonstrate that this region of the D4 receptor can interact with a large variety of SH3 domains of different origin. The strongest interactions were seen with the SH2-SH3 adapter proteins Grb2 and Nck. The repeat sequence itself is not essential in this interaction. The data presented indicate that the different SH3 domains in the adapter proteins interact in a cooperative fashion with two distinct sites immediately upstream and downstream from the repeat sequence. Removal of all the putative SH3 binding domains in the third intracellular loop of the dopamine D4 receptor resulted in a receptor that could still bind spiperone and dopamine. Dopamine could not modulate the coupling of these mutant receptors to adenylyl cyclase and MAPK, although dopamine modulated receptor-G protein interaction appeared normal. The receptor deletion mutants show strong constitutive internalization that may account for the deficiency in functional activation of second messengers. The data indicates that the D4 receptor contains SH3 binding sites and that these sites fall within a region involved in the control of receptor internalization. 相似文献
85.
EM Van der Aa IJ Meuwsen AC Boersen AC Wouterse JH Copius Peereboom-Stegeman FG Russel 《Canadian Metallurgical Quarterly》1994,15(3):279-289
The mechanism of uptake of p-aminohippurate (PAH) by syncytial microvillous membrane vesicles of human term placenta was investigated. Initial PAH uptake and efflux were increased in the presence of a pH-gradient and a Cl(-)-gradient, respectively. Forced negative and positive membrane potentials did not influence the uptake, which indicated that the transport is not electrogenic. The pH-dependent increase is probably the result of a higher rate of diffusion due to a lower degree of dissociation of PAH. Because several organic anions failed to transstimulate PAH uptake and FCCP did not decrease the uptake in the presence of an inwardly directed H(+)-gradient, ruling out a PAH/OH- antiport, an anion exchange system does not appear to be present in these membranes. Since electrogenicity and anion exchange seem not to be involved in the Cl(-)-dependent increase, an allosteric effect of Cl- on the transporter might be possible. Various organic anions were able to inhibit pH-stimulated PAH uptake significantly. Kinetic analysis of the probenecid sensitive part of uptake provided further evidence for mediated transport of PAH (Km = 7.4 +/- 2.6 mM and Vmax = 2.0 +/- 0.4 nmol/mg/15 s). Non-inhibitable diffusion accounted for the main part of total transport. Concentration dependent inhibition of PAH transport by probenecid showed a Ki of 2.5 +/- 0.9 mM. It is concluded that human placental syncytial microvillous membrane vesicles possess a low affinity transport mechanism for PAH with low specificity. The importance of this system, for placental excretion of anionic drugs, will depend on the intrasyncytial concentration of these drugs, caused by the transport across the basal membrane. 相似文献
86.
87.
International Journal of Computer Vision - 相似文献
88.
An overview of ultra-wideband microwave imaging via space-time beamforming for early-stage breast-cancer detection 总被引:1,自引:0,他引:1
Xu Li Bond E.J. Van Veen B.D. Hagness S.C. 《Antennas and Propagation Magazine, IEEE》2005,47(1):19-34
Ultra-wideband (UWB) microwave imaging has recently been proposed for detecting small malignant breast tumors. In this article, we review the current research status of this approach. First, we introduce the concept of microwave imaging via space-time (MIST) beamforming and related signal-processing algorithms. The objective of these signal-processing techniques is to form a spatial image of scattered microwave energy, and to identify the presence and location of malignant lesions from their scattering signatures. Next, we present numerical studies based on finite-difference time-domain simulations to demonstrate the efficacy of MIST beamforming for detecting small malignant breast lesions in both prone and supine configurations. Finally, the experimental feasibility of UWB microwave imaging is demonstrated using an initial imaging prototype and multilayered breast phantoms. 相似文献
89.
Wisse M. Feliksdal G. Van Frankkenhuyzen J. Moyer B. 《Robotics & Automation Magazine, IEEE》2007,14(2):52-62
In this article, we presented our passive-based biped Denise. Using only two foot contact switches as sensors and simple on/off pneumatic muscle action, it walks at 0.4 m/s and can handle floor disturbances up to 6 mm (leg length is 0.7 m). Its simplicity, efficiency, and die natural look of its motions make it a promising lead for the development of commercially viable humanoid robots. The aim of this article is to provide other researchers enough details so that they can reproduce the work or use it as a basis for future research. 相似文献
90.
An adaptable die is one that not only produces the correct geometrical shape, but also is designed through an adaptable method to impart other desirable properties to the product or process. In this first part of a series of papers, six kinematically admissible velocity fields are developed for use in upper bound models for axisymmetric extrusion through various dies, including extrusion through adaptable dies. Three base velocity fields are presented:
- (1) assuming proportional angles in the deformation zone,
- (2) assuming proportional areas in the deformation zone, or
- (3) assuming proportional distances from the centerline in the deformation zone.